1. Technical Field
The present invention relates to a power-supply control device, and particularly relates to a power-supply control device that is suitably used to control a power supply of an electric-powered vehicle.
2. Related Art
Two types of batteries, namely, a high-voltage battery and a low-voltage battery are usually provided in an electric-powered vehicle such as an EV (Electric Vehicle), an HEV (Hybrid Electric Vehicle), or a PHEV (Plug-in Hybrid Electric Vehicle).
The high-voltage battery is mainly used as a power supply for a load of a high voltage (hereinafter, referred to as a high-voltage load) such as a main power motor for driving wheels of the electric-powered vehicle to travel and a compressor motor of an air conditioner.
On the other hand, the low-voltage battery is mainly used as a power supply for a load of a low voltage (hereinafter, referred to as a low-voltage load) such as various ECUs (Electronic Control Units) that control units of the electric-powered vehicle, EPSs (Electric Power Steerings), electric brakes, car audio devices, windshield wipers, and power windows, and an illumination lamp.
For example, in order to charge the low-voltage battery, a DC-DC converter transforms the voltage of the high-voltage battery and supplies the voltage to the low-voltage battery.
When a remaining amount of the low-voltage battery becomes a predetermined value or less because the electric-powered vehicle is left for a long time, that is, when so-called battery run-out has occurred, a control system of the electric-powered vehicle cannot be operated irrespective of the remaining amount of the high-voltage battery, and therefore the electric-powered vehicle cannot be started.
Therefore, in order to prevent the run-out of the low-voltage battery in the case of leaving the HEV for a long time, there is proposed that the charge is performed from the high-voltage battery to the low-voltage battery at regular time intervals while an ignition switch is turned off (for example, see Japanese Unexamined Patent Publication No. 2006-174619).
There is also proposed that the high-voltage battery is directly connected to an input of a DC-DC converter control circuit that controls the DC-DC converter without interposing a relay, the DC-DC converter is started up to be able to charge the low-voltage battery even if the low-voltage battery has run out (for example, see Japanese Unexamined Patent Publication No. 2006-50779).
A control device of the electric-powered vehicle includes the high-voltage battery, a booster that boosts up the voltage of the high-voltage battery to output the voltage onto a generator motor side, a step-down device that steps down the voltage supplied from the generator motor or the high-voltage battery to supply the voltage to the low-voltage battery, a first switch that is provided in one of positive and negative electrodes of the high-voltage battery, and a second switch that is provided in the other of the positive and negative electrodes. In the control device, a power supply line for the step-down device is connected between the first switch and the booster and between the second switch and the high-voltage battery. There is also proposed that the run-out of the low-voltage battery is prevented such that, when the generator motor breaks down, the low-voltage battery is continuously charged by the high-voltage battery through the step-down device while the step-down device is protected by turning off the first switch and such that, when the high-voltage battery breaks down, the low-voltage battery is continuously charged by the generator motor through the step-down device while the step-down device is protected by turning off the second switch (for example, see Japanese Unexamined Patent Publication No. 2007-28803).
There is also proposed a vehicle power supply that supplies the power to a low-voltage system through the DC-DC converter while supplying the power to a high-voltage system from the high-voltage battery, in which a capacitor is charged when a relay switch that opens and closes connection among the high-voltage battery, the high-voltage system and the DC-DC converter, and the relay switch is turned on to be able to start up the high-voltage system and the low-voltage system using the power of the capacitor when the ignition switch is turned on, thereby eliminating the low-voltage battery (for example, see Japanese Unexamined Patent Publication No. 2005-287242).
In starting the supply of the power from the high-voltage battery to each load, when abnormalities are generated in the high-voltage battery, a voltage equal to or more than a rated voltage may be applied to each load including the DC-DC converter, thereby causing breakdown.